1. Field of the Invention
The present invention relates to a transfer apparatus for use with standardized mechanical interface (SMIF) systems for facilitating semiconductor wafer fabrication, and in particular to a plate for supporting a side opening pod adjacent to a processing station, which plate is capable of controlled rotation and/or translation to position the pod at a desired orientation with respect to a side opening interface of the processing station.
2. Description of the Related Art
A SMIF system proposed by the Hewlett-Packard Company is disclosed in U.S. Pat. Nos. 4,532,970 and 4,534,389. The purpose of a SMIF system is to reduce particle fluxes onto semiconductor wafers during storage and transport of the wafers through the semiconductor fabrication process. This purpose is accomplished, in part, by mechanically ensuring that during storage and transport, the gaseous media (such as air or nitrogen) surrounding the wafers is essentially stationary relative to the wafers and by ensuring that particles from the ambient environment do not enter the immediate wafer environment.
The SMIF system provides a clean environment for articles by using a small volume of particle-free gas which is controlled with respect to motion, gas flow direction and external contaminants. Further details of one proposed system are described in the paper entitled "SMIF: A TECHNOLOGY FOR WAFER CASSETTE TRANSFER IN VLSI MANUFACTURING," by Mihir Parikh and Ulrich Kaempf, Solid State Technology, July 1984, pp. 111-115.
Systems of the above type are concerned with particle sizes which range from below 0.02 microns (.mu.m) to above 200 .mu.m. Particles with these sizes can be very damaging in semiconductor processing because of the small geometries employed in fabricating semiconductor devices. Typical advanced semiconductor processes today employ geometries which are one-half .mu.m and under. Unwanted contamination particles which have geometries measuring greater than 0.02 .mu.m substantially interfere with 0.3 .mu.m geometry semiconductor devices. The trend, of course, is to have smaller and smaller semiconductor processing geometries which today in research and development labs approach 0.2 .mu.m and below. In the future, geometries will become smaller and smaller and hence smaller and smaller contamination particles become of interest, including molecular contaminants.
A SMIF system has three main components: (1) minimum volume, sealed pods used for storing and transporting wafer cassettes; (2) a minienvironment surrounding cassette ports and wafer processing areas of processing stations so that the environments inside the pods and minienvironment (upon being filled with clean air) become miniature clean spaces; and (3) a transfer mechanism to load/unload wafer cassettes and/or wafers from the sealed pods to the processing equipment without contamination of the wafers in the wafer cassette from external environments.
There are, in general, two types of SMIF pods. One type is a bottom opening pod comprising a pod door at the bottom of the pod which sealably mates with a pod top. A wafer-carrying cassette may be stored and transported within the pod, with the cassette resting on the pod door. A second type of pod is a side-opening pod comprising a container sealably mating with a vertically oriented door on a side of the pod. The container may house a wafer-carrying structure or cassette, or in the alternative, the container itself may be formed with a plurality of slots for supporting the wafers directly therein.
Conventionally, in order to transfer wafers from a side-opening SMIF pod to within a particular processing station, the pod is loaded onto a support plate which is supported adjacent a front-opening interface port of a minienvironment. The support plate is generally mounted on a shelf extending from an outer wall of the minienvironment. The pod and the interface port are designed so that the pod door overlies a port door covering the front-opening interface port, and an outer circumference of the pod container overlies a port plate surrounding the port door. Once located adjacent to the interface port, mechanisms within the interface port release and separate the pod door from the container. Thereafter, the pod door and port door are drawn into the minienvironment, and lowered or otherwise moved away from the access path to the wafers within the pod.
Once the pod doors are moved away, a wafer transfer mechanism within the minienvironment may transfer wafers between the pod and the processing station. One example of a wafer transfer mechanism is a 2-arm pick and place robot 20 shown in FIG. 1A. The 2-arm robot comprises a central shaft 22 mounted for rotation and translation along a z-axis concentric with the shaft axis of rotation. The robot further includes a first arm 24 affixed to an upper end of the shaft for rotation with the shaft, and a second arm 26 pivotally attached to the opposite end of the first arm. The pick and place robot further includes an end effector 28 for gripping individual wafers 30 from within a pod 32. The robot is controlled by a computer such that the end effector may be controllably moved about in three-dimensional space to access and transfer each of the wafers within the container. For applications where the side-opening pod includes a separate wafer-supporting cassette therein, the pick and place robot may further include a precision gripping mechanism mounted at the free end of the second arm for gripping and transferring the cassette between the pod and the processing chamber.
Another type of wafer transfer mechanism is a 3-arm, pick and place robot 34 such as shown in FIG. 1B. Such a robot operates similarly to the 2-arm robot 20, but includes three arms 36, 38, 40 operating with an end effector 28. In general, 2-arm pick and place robots are more desirable than 3-arm robots in that the 2-arm robots are more reliable and faster than the 3-arm robots.
The Semiconductor Equipment and Materials International ("SEMI") standard for the semiconductor industry with regard to positioning side-opening pods adjacent to processing and testing stations requires that a pod be located at a front of the processing/testing station with an edge of the pod provided parallel to the front of the station. This standard has been set so that a robotic handler may transfer a SMIF pod onto the translating support plate adjacent to a processing or testing station without requiring customization of the robotic handler or special manipulation of the SMIF pod. As explained hereinafter, such a requirement greatly limits the design flexibility with regard to transfer of wafers into the processing station, and requires a relatively large footprint for the transfer system.
Referring to FIG. 1A, there is shown a minienvironment 23 including a front-opening interface port 25, a 2-arm pick and place robot 20, and a processing station 42. A front-opening pod 32 is seated on a translating support plate (not shown) mounted in shelf 37 extending out from the minienvironment. A reference axis 21 corresponding to the axis of travel of end effector 28 in the 2-arm robot is designed to pass through the rotational center of the robot at shaft 22. Moreover, the axis of travel of the end effector 28 must be substantially perpendicular to the opening of the pod 32 in order for wafers 30 to be inserted or removed through the pod opening. Therefore, in applications transferring wafers from a single pod 32 into process chamber 42, a 2-arm robot may be used, but the robot must be placed directly in front of the pod.
A consequence of this alignment is that the front-opening interface port 25 must also be provided parallel to the front of the station, so that the pod can properly interface with the port. Additionally, processing and testing stations typically include other components in addition to the pick and place robot and translating support plate, such as for example keyboards, CRTs, and other electronic assemblies. The requirement that the pod be placed parallel to and at the front of a station severely limits the design flexibility of the processing station and controls. Further still, it is expensive to maintain clean room environments, and it is very important to minimize the space within the minienvironment 23. Having to locate the pick and place robot directly in front of the pod increases the depth (i.e., along reference axis 21) of the footprint of minienvironinent 23.
It is often desirable to process more than one pod at a processing station at the same time. In order to accomplish this, a 3-arm robot must be used (as shown in FIG. 1B), with an accompanying sacrifice in speed and reliability. Alternatively, a 2-arm robot may be mounted on a track (not shown) so that the robot can move back and forth parallel to the front of the minienvironment to access wafers from the two pods. Again, this requires a lot of time and adds another source of positional variance to the system. Moreover, as described above, such a system requires a relatively large footprint.